1. Field of the Invention
The present invention generally relates to an electronic device. In particular, the present invention relates to an electronic device in which a commercial power supply is used, and which has a power supply circuit that supplies operating power to a load circuit.
2. Background Information
Conventional electronic devices such as television receivers and video recorders are operated by supplying operating power to some of the functions even when the main power is switched off, so that the operation of the electronic devices can be commenced in response to a power on signal or the like sent from a remote control device. A state in which the main power is off is called a standby state. With this type of electronic device, apart from the main device that controls the operation of the load circuit, there is also provided a power supply controlling microprocessor that controls the supply and shut-off of operating power to the various parts of the electronic device including the main device (See Japanese Laid-Open Patent Application Publication Nos. 2002-318624, 2000-125372, 2000-47764, for example). Also, the power supply controlling microprocessor operates regardless of whether the main power supply is on or off. In other words, the power supply circuit supplies operating power to the power supply controlling microprocessor regardless of whether the main power supply is on or off. Also, the power supply controlling microprocessor has a function of processing control signals sent from a remote control device. Further, the power supply controlling microprocessor monitors for the occurrence of abnormalities in the power supply circuit (i.e., power supply abnormalities), and if an power supply abnormality should occur, the microprocessor has the function of directing the power supply circuit to shut off the output of operating power to the load circuit (e.g., cut off the commercial power supply), among other such functions.
However, it is possible for the power supply controlling microprocessor to be built into a main device in order to lower the cost of an electronic device. With a conventional device in which the power supply controlling microprocessor is provided separately from the main device, upon input of a commercial power supply (e.g., upon connection), there is no problem as long as operating power is always supplied to the power supply controlling microprocessor. Specifically, there is no problem with a constitution in which the supply of operating power to the power supply controlling microprocessor is commenced when the commercial power supply is connected, and the supply of operating power to the load circuit or main device is controlled by the power supply controlling microprocessor with respect to the power supply circuit after the start-up of the power supply controlling microprocessor.
On the other hand, with a constitution in which a power supply controlling microprocessor is built into a main device, the power supply controlling microprocessor can not load programs from memory unless operating power is also supplied to the main device upon input of the commercial power supply. Specifically, with the constitution in which the power supply controlling microprocessor is built into the main device, operating power has to be supplied to the main device as well, and not just to the power supply controlling microprocessor, upon input of the commercial power supply. With a constitution in which operating power is constantly supplied to the main device as well upon input of the commercial power supply (e.g., upon connection), the operating power ends up being supplied to the main device when the electronic device is in standby mode, and this means that some of the power consumption by the electronic device is wasted. Also, even if the occurrence of a power supply abnormality in the power supply circuit is detected, the supply of operating power to the main device cannot be shut off.